The present invention relates to transmission of sensory information obtained by a prosthetic device to the brain to create a sensory perception. In particular, the present invention relates to the transmission of visual, audile, or tactile information to the brain in an encoded form that causes a functionally related perception on the part of the subject.
In normal circumstances, a healthy human being receives a stimulus from the external environment that is detected by the appropriate type of receptor. For example, photoreceptors within the eye detect light with each photoreceptor converting the received stimulus into neuron impulses. This conversion of the stimulus energy into neuron impulses takes place in one or more neurons that are associated with the receptor. Each neuron then emits a neuron spike sequence that is used by the brain to obtain sensory perception. The combination of many neurons, each transmitting many neuron spike trains provide a complete or global sensory perception.
It is known that a simulated neuron spike or pulse train can produce a sensory perception in a subject when applied to selected areas of the brain, spinal column, or nerves of a subject. Additionally, the brain has been `mapped` so that specific locations on or within the brain are associated with specific sensory perceptions. Placement of an electrode at an appropriate location and stimulation with electrical pulses will produce a sensory perception. For example, an electrode placed on the striate cortex and to which a simulated neuron impulse train is transmitted will cause some type of visual perception.
Repeated pulses to a specific location, such as the striate cortex, will produce some type of perceivable image. However, meaningful information as to form, luminescence, and color is not conveyed. It is presently believed that the informational content for all dimensions of a sense have their basis in a coding scheme that is based upon the number of neuron impulses that occur during a predetermined interval, for example, a greater number of neuron impulses are believed to be a function of a more intense perceived parameter. However, this coding scheme only allows one dimension of a sense to be coded by each neuron. Proponents of this coding scheme believe that the large number of neurons contain a distribution among them that allows the various dimensions of sense to be recognized so that perception can take place. However, it has not been possible to determine how these various dimensions are recognized using this population coding scheme. It has not been possible to develop a prosthetic device using this population coding principle which can sense an external stimulus and transmit information to the brain so that meaningful sensory perception can take place.